SUMMARY Over 100 new HIV infections occur each day in the US, yet current rapid diagnostic tests (RDTs) that screen for HIV cannot detect acute HIV infections (AHIs) during the first weeks and months when newly infected individuals are the most likely to spread the virus to others. Further, people who use drugs (PWUD) are 22 times more likely to acquire HIV than the average population and face social, geographical, and institutional barriers that limit their access to HIV testing and care. To overcome this challenge at the nexus of substance abuse and HIV, there is an urgent need for a radically new approach to diagnose AHIs in order to engage PWUD in the care continuum at the earliest stages of infection and prevent transmission of HIV. Building on our preliminary work, we will combine current HIV p24-based RDTs detection strategies with isothermal loop-mediated nucleic acid amplification (LAMP) enabling highly sensitive detection of HIV. We will then integrate this into a robust and user-friendly handheld AHI testing platform. Targeting the highly abundant p24 antigen and leveraging this to initiate LAMP will improve sensitivity over RDTs by >2000x. This addition of an amplification control will provide clinically relevant differentiation of invalid tests from false negative tests. As with current RDTs, this entire process will require only 3 simple steps for the user: First, a drop of blood is added to the sample pad. Next, the user dispenses a buffer solution. After a brief waiting period, the user reads the visual yes/no result. The success of this, and all technology platforms will depend on adoption by, and delivery to, PWUD and others involved in their treatment. We will work with PWUD, community health workers, substance abuse treatment centers, harm reduction partners, and public health departments to perform community-based participatory research into the existing barriers to HIV testing and care faced by PWUD. Early assessment of device feasibility, acceptability, and usability by these same partners will ensure that the handheld AHI test will be readily adopted by stakeholders. In partnership with the Third Coast Center for AIDS Research in Chicago, we will evaluate our proof-of-concept device against clinical performance metrics in plasma and whole blood. The successful completion of this work will produce a user-approved field-ready AHI tests capable of detecting the equivalent of <1000 HIV virons/mL from a finger prick blood sample within 30 minutes. This new testing paradigm would transform the HIV care continuum by making critical AHI detection possible in the field, at sites ranging from substance abuse treatment facilities to syringe services programs. The platform developed in this work will lay the foundation for providing PWUD with targeted interventions that meet their needs and remove barriers to HIV care as well as additional diagnostics such as rapid Hepatitis C detection.